JP3287197B2 - Threaded fittings for oil country tubular goods - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a threaded joint for an oil country tubular good used for exploration and production of natural gas and crude oil buried underground. In particular, the joint is suitable for pumping a gas or oil containing a large amount of corrosive impurities under high pressure at a high depth.

[0002]

2. Description of the Related Art Today, threaded joints are widely used as joints for connecting oil country tubular goods used for exploration and production of natural gas fields and oil fields having a depth of several thousand meters. There are two types of threaded joints for oil country tubular goods. Integral method for connecting tubes with a pin at one end and a box at the other end, and coupling method for connecting a coupling with two box portions and a tube with pin portions at both ends It is.
These threaded joints are required to have the following performance in common.

[0003] Withstands the tensile force in the axial direction due to the weight of the connected pipe, withstands the internal pressure of the internal fluid or the external pressure of the external fluid, can be used repeatedly for several tens of times, corrosion by the internal and external fluids And withstand erosion.

In recent years, wells have become deeper and are often used in harsh environments such as polar regions. Furthermore, deposits containing a large amount of corrosive and oxidizing impurities, which have not been targeted so far, have been mined, and the performance of joints has rapidly advanced in order to meet the above-mentioned requirements.

FIG. 3 is a drawing showing a coupling type joint having a seal portion and a torque shoulder portion, showing an example of a threaded joint for oil country tubular goods in the case of an inner shoulder. FIG.
(A) is a figure showing the state which fastened the coupling with the pipe main body. FIG. 3B is a drawing showing the screw portion, the seal forming portion and the torque shoulder forming portion of FIG. 3A.

The "torque shoulder portion" is used to control the fastening torque to an appropriate value by abutting the surfaces on which the torque shoulders are formed, so that a high contact pressure enough to cause plastic deformation is not generated in the seal portion. It is provided in. "Inner surface shoulder" refers to a joint type having torque shoulder forming portions 14, 24 on the inner surface side of the pipe, or a portion of the torque shoulder.

FIG. 2 is a drawing showing an example of a threaded joint for an oil country tubular good having both an inner shoulder and an outer shoulder. FIG.
(A) is a drawing showing a section of a pipe and a coupling after fastening. FIG. 2B is a drawing showing the inclination of the torque shoulder forming surfaces on the pin side and the box side forming the outer surface shoulder. The “outer surface shoulder” refers to a joint type or a torque shoulder portion that forms a torque shoulder portion by abutment of the torque shoulder formation surface 64 at the box-side tip against the torque shoulder formation surface 54 at the root of the external thread on the outer surface of the tube. .

In the following description, unless otherwise noted,
The joint is a coupling type inner shoulder joint having a seal portion and a torque shoulder portion.

In FIG. 3B, a male screw 12 provided at the distal end of the tube 10 and a female screw 22 provided inside the coupling 20 are screwed together. A seal forming surface 13 which is a rotating surface of a tapered curve or an arc having a large radius of curvature at a tip end of the pin portion 11, and a seal forming surface 2 which is a rotating surface of a tapered curve which is a screwing root of the box portion 21.
3 and forms a seal portion by contacting at the time of fastening. Here, the term “tapered curve” refers to a curve that is in a plane including the pipe axis (also the axis of the coupling) and that becomes closer to the pipe axis as it approaches the center of the box. The “rotational surface” refers to a curved surface formed by rotating the tapered curve or the arc around the pipe axis (which is also the axis of the coupling).
By forming a metal seal with this seal portion, airtightness is maintained against the internal pressure due to the fluid inside the oil country tubular good or the external pressure due to the fluid outside the pipe.

The pin-side torque shoulder forming surface 14 at the further tip of the seal forming surface 13 and the torque shoulder forming surface 24 at a portion closer to the box center of the box-side seal forming surface 23 are brought into contact with each other so that the torque shoulder is formed. Form a part.

In addition to hermetic performance against high-pressure fluid, a thread joint for an oil country tubular good must also have corrosion resistance to crevice corrosion, which may lead to leakage or breakage from the thread. Crevice corrosion is a phenomenon in which a corrosive fluid penetrates into minute gaps between a pin member and a box member, stays and concentrates, and a member in a high stress load state inside a joint exposed to this fluid is condensed. Phenomena, such as general corrosion and stress corrosion cracking. Crevice corrosion does not occur unless there is a minute gap on the inner surface or outer surface of the pipe where the corrosive fluid exists.

In order to meet the above demands, the following seal-shaped and torque-shoulder-shaped joints have been proposed in which the joint shown in FIG. 3 is improved. These are α)
Joints that cover the contact surface with a soft material, β) Joints using packing, γ) Joints that increase the airtightness of the seal part by elastic deformation of the pin tip, δ) Seal parts by devising the contact of the torque shoulder forming surface Are classified roughly into four types of joints with improved airtightness.

Α) There is a joint proposed in JP-A-56-109975 and JP-A-1-199088, in which the seal forming surfaces on the pin side and the box side are covered with a soft metal or the like. This is by contacting the seal forming surface and the torque shoulder forming surface covered with a soft material,
The sealing effect of the seal portion and the torque shoulder portion is improved.

[0014] However, this method has a drawback that the sealing material is dropped or worn during repeated fastening and releasing of the joint, so that the hermetic performance is lowered and the method cannot withstand several tens of uses.

FIG. 4 shows a joint disclosed in Japanese Utility Model Application Laid-Open No. 58-142475, in which a ring-shaped soft material is provided between the pin-side torque shoulder forming surface 14 and the box-side torque shoulder forming surface 24. It is a figure showing the joint which inserted the packing 30 which becomes. In FIG.
A value of 0 allows variations in the tightening length of the pin 11 in the axial direction. For this reason, the seal forming part is always fitted with a constant contact pressure by the fastening by the torque management without being influenced by the manufacturing tolerance of the seal forming part, and stable airtight performance can be obtained.

[0016] This joint has a problem that it requires labor and cost at the time of production such as production and insertion of packing. further,
Originally, this joint does not have the function to control the fastening torque to an appropriate value, which is required for the torque shoulder part, so it is necessary to strictly manage the torque when fastening on site, and the handling is deteriorated. Leads to. Further, there is a problem that a gap is generated between the packing and the torque shoulder surface due to a manufacturing error, and crevice corrosion occurs.

FIG. 5 shows a joint disclosed in Japanese Patent Application Laid-Open No. 60-26878, in which a thin tip of a pin portion (lip portion) is used to provide high sealing performance by utilizing elastic deformation. FIG. FIG. 5A shows the seal forming surface and the torque shoulder forming surface of each of the pin portion and the box portion before fastening. FIG. 5B shows the contact pressure distribution of the seal portion and the torque shoulder forming portion after fastening. This joint has a smooth groove 3 on the inner surface of the pipe over the pin tip lip 15 and the box side torque shoulder.
Has 1. Further, the inclination θ _{2 of} the box-side torque shoulder surface 24 is larger than the inclination θ _{1 of the} pin-side torque shoulder surface 14, and the effective diameter of the pin-side seal formation surface 13 is smaller than the effective diameter of the box-side seal formation surface 23. Since the pin tip lip portion 15 has a small thickness due to the groove 31, elastic deformation easily occurs. Pin shoulder torque shoulder surface 1 by screwing
4 is strongly pressed against the box-side torque shoulder surface 24, the seal forming surface 13 near the center of the pin tip lip 15 bulges outward due to the difference in inclination. Therefore, the sealing surface 32 is formed by contacting the box-side seal forming surface 23. As a result, there are two sealing surfaces: the sealing surface 33 of the torque shoulder forming portion formed by pressing and the sealing surface 32 of the sealing portion.

This joint is similar to the structure of the present invention in that the inclination θ ₁ of the pin-side torque shoulder forming surface 14 is slightly smaller than the inclination θ _{2 of} the box-side torque shoulder forming surface as shown in FIG. ing. However, the difference θ ₂ −θ _{1 in} the inclination of the torque shoulder portion is due to the thin pin tip lip portion 15 pressed against the box side torque shoulder forming portion 24.
It is provided to inflate the center of. Since the pin-side seal forming surface 13 comes into contact with the box-side seal forming portion 23 only after the bulging deformation occurs, the effective diameter of the pin-side seal forming surface is smaller than that on the box side. The present joint and the joint of the present invention to be described later are different in the above two points.

In the present joint, in order to obtain a sealing surface having a sufficient contact pressure at the seal forming portion, a large bending deformation of the pin tip lip portion must be realized. For that purpose, the pin tip lip must be pressed against the box-side torque shoulder forming surface with a very large force. For this reason, there is a problem that excessive plastic deformation occurs particularly in the portion 26 near the tube inner surface of the box-side torque shoulder forming surface, and the predetermined airtightness cannot be exhibited.

Δ) FIG. 6 shows a joint disclosed in Japanese Patent Application Laid-Open No. 52-11765, in which the outer diameter direction of the tube generated near the tip of the pin portion due to the contact between the pin side and the torque shoulder forming surface on the box side. 3 is a drawing showing a joint in which the sealing performance of a sealing portion is enhanced by bulging into a groove. Pin side seal forming surface 1
3 is an arc-shaped rotating surface having a large radius of curvature, and the box-side seal forming surface is a conical surface (tapered linear rotating surface).
And The pin-side torque shoulder forming surface 14 and the box-side torque shoulder forming surface 24 are provided with different curvatures R _2.
And a convex curved surface and concave surface having a R _3. The radius of curvature R ₂ of the pin-side torque shoulder forming face takes less than the radius of curvature R ₃ of the box side torque shoulder forming face, and R
The radius of curvature center positions of _2, it from the tube side of R _3.
With this structure, the deflection of the pin-side lip portion 15 in the direction of the inner surface of the tube is reduced, and the uneven contact pressure in the circumferential direction of the seal portion due to a manufacturing error is automatically redistributed to a uniform contact pressure.
For this reason, a good sealing state can be obtained at two places, the torque shoulder part and the seal part.

In this joint, the contact of the torque shoulder portion is
Maintained by circumferential line contact at portions 16 and 26 near the tube inner surface. For this reason, there is a problem that the contact pressure at this portion becomes extremely high, and excessive plastic deformation occurs as in the case of the above γ), thereby lowering the airtightness.

[0022]

SUMMARY OF THE INVENTION The present invention provides a joint which maintains a high degree of airtightness even after repeated use for several tens of times without causing crevice corrosion without increasing the production cost and deteriorating the handleability. The task was to do.

[0023]

In order to solve the above-mentioned problems of the conventional joint, the present inventor has proposed a method of forming a seal portion and a torque shoulder portion when a joint is fastened and when a tensile stress is further applied in an axial direction. The behavior was examined in detail, and the following was confirmed.

1) The seal portion of the threaded joint for oil country tubular goods usually has an effective diameter of the pin-side seal forming surface 13 larger than an effective diameter of the box-side seal forming surface 23 and generates a contact pressure by fitting the two. To form an airtight metal seal. Here, the “effective diameter” of the pin-side seal formation surface and the box-side seal formation surface is the diameter of the “reference position” defined on each seal formation surface in a state before fitting.
That is, it is twice the average distance from the tube axis or box axis to the "reference position" of each seal forming surface.
The "reference position" is defined as "the portion where the pin-side and box-side seal forming surfaces are in contact with each other when the fastening is completed."
And the “position before mating”
Point out.

2) Due to the difference in the effective diameter, stress acts on the pin side in the diameter reducing direction. In particular, bending deformation occurs at the tip of the pin.

FIG. 7 is a view showing a state in which the pin-side torque shoulder forming surface is inclined by θa with respect to the box-side torque shoulder forming surface due to the diameter reduction deformation occurring on the pin-side seal forming surface. As shown in the figure, in the case of a joint in which a seal forming portion and a torque shoulder forming portion are arranged near the tip of the pin portion, the contact pressure generated in the seal forming portions 13 and 23 at the time of fastening causes the pin tip lip portion 15 to move. Bending deformation occurs in the direction of diameter reduction. Due to this bending deformation, the pin-side torque shoulder forming surface 14 is inclined to the inner surface side of the pipe by θa with respect to the box-side torque shoulder forming surface 24.

3) In a normal joint in which the torque shoulder forming surfaces on the pin side and the box side have the same inclination, the contact pressure at the pipe inner surface side portions 16 and 26 of the torque shoulder portion is small due to the bending deformation described above. . For this reason, when a large tensile stress acts on the pipe body including the joint in the fastened state, the contact pressure almost disappears, and in some cases, a gap is formed in the inner portion of the torque shoulder.

4) A difference is previously provided between the inclination of the pin-side torque shoulder forming surface and that of the box side, and after bending deformation due to fitting, the torque shoulders on both sides are flush with each other or slightly overlap on the inner surface side of the pipe. If the inclination of the forming surface is adjusted, a desirable contact pressure distribution is obtained.

Based on these results, the oil country tubular good threaded joint of the present invention was completed.

FIG. 1 is a diagram illustrating the structure of the inner surface shoulder vicinity of smaller than the inclination theta ₂ of the inclination theta ₁ of the pin-side torque shoulder forming face box side torque shoulder forming face. FIG. 1A is a drawing showing a seal portion and a torque shoulder forming portion on the pin side and the box side of the joint before fastening. FIG. 1B is a diagram showing a distribution of contact pressure (calculation results) generated in the seal portion and the torque shoulder portion after fastening. From the figure, it can be seen that a uniform contact pressure can be obtained by anticipating the bending deformation of the pin-side torque shoulder forming surface and reducing the inclination of the pin-side torque shoulder forming surface accordingly.

The invention also applies to the case of external shoulders. As shown in FIGS. 2 (a) and 2 (b), the technical idea of obtaining a uniform contact pressure by providing a difference in the inclination of the torque shoulder forming surface also holds true for the external shoulder.

Here, the gist of the present invention is a structure of an oil country tubular goods joint in which durability and airtightness are enhanced by providing a difference in the inclination of a torque shoulder forming surface between a pin side and a box side as described below. (See FIGS. 1 and 2) (1) As shown in FIG. 1, a seal forming surface 13 provided on the outer surface of the tip of the pin portion 11 having a male screw, and a seal provided on the inner surface of the box portion 21 having a female screw. By forming a seal portion by fitting with the forming surface 23, the torque shoulder forming surface 14 provided at the foremost portion of the pin and the corresponding torque shoulder forming surface 24 provided on the box side are abutted. A threaded joint for oil country tubular goods having the following features that forms an inner shoulder.

(A) The pin-side and box-side seal forming surfaces are each composed of a rotating surface.
The effective diameter of No. 3 is larger than the effective diameter of the box side seal forming surface 23.

(B) The inclination θ ₁ of the pin-side torque shoulder forming surface is slightly smaller than the inclination θ ₂ of the box-side torque shoulder forming surface, and the difference (θ) between the two is 0.5 ° ≦
θ ≦ 4.0 ° is satisfied. Where θ = θ ₂ −θ ₁

The effective diameter is, as described above, the value before fitting.
Of the reference position defined on each seal forming surface in the state of
Diameter, ie from tube axis or box axis respectively
Twice the average distance to the reference position of the seal forming surface
U. When the fastening is completed, the reference position is
Where the seal-forming surfaces on the
And means the position in the state before mating.
You.

(2) As shown in FIG. 2, a seal forming surface 53 provided on the outer surface of the root of the pin having the male screw and a seal forming surface 6 provided on the inner surface of the tip of the box having the female screw.
3 to form a seal portion, and a torque shoulder forming surface 64 provided at the forefront of the box and a corresponding torque shoulder forming surface 54 provided on the outer surface of the corresponding pin root are brought into contact with each other. A threaded joint for oil country tubular goods having the following characteristics.

(A) The pin-side and box-side seal forming surfaces are each composed of a rotating surface.
The effective diameter of 3 is larger than the effective diameter of the box-side seal forming surface 63.

(C) The inclination θ ₁ of the pin-side torque shoulder forming surface is slightly larger than the inclination θ ₂ of the box-side torque shoulder forming surface, and the difference (θ) between the two is 0.5 ° ≦ θ ≦ 4. .0 °. However, θ = θ ₁ −θ ₂ (3) Furthermore, the above (1) having the following features (d)
Or threaded joint for oil country tubular goods of (2). (D) the difference between the inclination theta ₂ of the inclination of the pin-side torque shoulder forming face theta ₁ and the box-side torque shoulder forming face theta is, D / t
And δr are substantially proportional to each other, and when the value of D / t or δr is large, the difference θ between the inclinations of the torque shoulder forming surfaces on the pin side and the box side is increased, and conversely, D / t or δr When the value is small, the difference θ in the inclination of the torque shoulder forming surface is reduced. Where D, t
And δr are as follows. D = outer diameter of pipe or coupling, t = wall thickness of pipe or coupling δr = (fitting distance of seal forming surface in radial direction) − (fitting distance of screw forming surface in radial direction)

However, D, t and δr are as follows.

D = coupling outer diameter, t = coupling thickness, δr = (fitting distance in the radial direction of the seal forming surface) − (fitting distance in the radial direction of the screw forming surface)

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for each limitation of the present invention will be described below.

1. The difference in inclination between the pin-side and box-side torque shoulder forming surfaces The pin-side seal forming surface is formed of a tapered curve or a rotating surface of an arc having a large radius of curvature. The box-side seal forming surface is formed by a rotating surface having a tapered curve.

The effective diameter of the pin-side seal forming surface must be larger than the effective diameter of the box-side seal forming surface. As described above, the effective diameter refers to the diameter of each reference portion of the pin-side seal forming surface and the box-side seal forming surface.

When fitting, the one that fits inside (pin side)
If the effective diameter of the pin is large, if the pin is forcibly fitted, the tip of the pin having a small rigidity must be reduced in diameter. When the pin tip deforms in diameter, the pin tip undergoes bending deformation toward the inner surface of the tube. Therefore, the inclination of the pin-side torque shoulder forming surface changes by the amount of the bending deformation (FIG. 7).
reference).

In the joint shown in FIG. 1A, the inclination θ ₁ of the pin-side torque shoulder forming surface 13 is smaller than the inclination θ _{2 of the} box-side torque shoulder forming surface 23 by θ (= θ ₂ −θ ₁ ). The angle difference θ is set to be equal to or slightly larger than the above-described change in inclination θa actually caused by bending deformation. As shown in FIG. 7, the inclination change θa due to the bending deformation actually occurring is determined by the deflection angle θ ′ of the pin-side torque shoulder portion 14 when the pin tip lip portion 15 is bent by the contact pressure of the seal forming portion. Is almost equivalent to Here, the deflection angle means the lip 15 at the tip of the pipe.
Refers to the angle at which the element is bent under a lateral load or bending moment.

The following contact pressure distribution can be obtained by making such an angle difference between the inclination of the torque shoulder forming surfaces of the pin portion and the box portion.

A substantially uniform contact pressure distribution over the entirety of the pin and box side torque shoulder forming surfaces 14 and 24, or as the contact pressure on the tube inner surfaces 16 and 26 increases and approaches the seal forming portions 17 and 27, Slowly decreasing contact pressure distribution Therefore, stress concentration does not occur so much as to cause excessive plastic deformation in the vicinity 16 and 26 of the inner surface of the torque shoulder portion on the inner surface of the pipe, and there is sufficient contact to prevent the formation of a gap in this portion. Pressure can be secured. For this reason, it can withstand dozens of uses,
And a threaded joint for oil country tubular goods which does not cause crevice corrosion can be obtained.

In this manner, the torque shoulder forming surfaces 14 and 24 on the pin side and the box side are provided with substantially uniform contact pressure.
Are in contact with each other, so that local plastic deformation due to stress concentration or the like does not occur. Therefore, when a tensile stress is applied to the pipe body including the joint fastened in this state, the contact pressure of the torque shoulder portion decreases almost uniformly over the entire surface, which is smaller than that of the conventional joint having the torque shoulder shape. The tensile load value at which the torque shoulder portion opens is much higher. Therefore, when the contact pressure at the time of fastening is sufficiently high, a torque shoulder portion that does not open even when a tensile stress equivalent to the yield strength of the pipe body is applied is formed, and excellent crevice corrosion resistance can be obtained.

[0049] Torque shoulder surface 1 on pin side and box side
In the joints having the same inclination of 4 and 24, the torque shoulder surface does not have a uniform contact pressure distribution, and the contact pressure on the seal forming side is high and that on the inner surface side of the pipe is low. As a result, when tensile stress such as its own weight is applied after fastening,
The contact pressure on the inner surface side is extremely small. In extreme cases, this part opens. When used for a long time in this state, the internal high-pressure and corrosive fluid permeates into the joint from the gap between the pipe inner surface side portions 16 and 26 of the torque shoulder portion. As a result, the seal portion and further the high stress load portion of the thread portion are corroded, and in the worst case, leakage occurs or the joint is broken. The joint of the present invention can prevent such a problem from occurring until after several tens of uses.

On the contrary, even when a compressive force is applied, the contact pressure of the torque shoulder portion is almost uniform over the entire surface.
Local plastic deformation due to stress concentration or the like is unlikely to occur in the torque shoulder portion, so that “excessive plastic deformation that cannot be used repeatedly” does not occur. Here, "it is impossible to use repeatedly" means, in particular, that the torque control and the function as a sub-seal cannot be performed due to permanent deformation of the torque shoulder on the box side, making it impossible to properly fasten the joint. Refers to the inability to demonstrate its performance.

The inclination difference θ must not be too large. If θ is too large, stress concentration occurs on the inner surface side of the torque shoulder portion, and local plastic deformation occurs. θ has an appropriate range as described later.

2. Appropriate range of inclination difference Pin-side seal forming surface 13 and box-side seal forming surface 23
Can be obtained by a calculation formula based on the classical shell theory. Furthermore, the correspondence between the deflection angle θ ′ obtained by this calculation formula and the actually generated change in inclination θa has been confirmed by experiments. Accordingly, by determining the deflection angle θ ′ at the tip of the pin, it is possible to determine the change θa in the inclination of the pin-side torque shoulder forming surface that actually occurs. A difference θ between the inclination of the pin-side torque shoulder surface and the inclination of the box-side torque shoulder surface is set to be equal to or slightly larger than the inclination change θa. The inclination difference θ depends on the size, thickness, fitting margin, mechanical properties of the joint material, etc. of the threaded joint for oil country tubular goods, but is 0.5 ° or more and 4.0 ° for the threaded type joint for oil country tubular goods in a practical range. The following can be set. here,
The term “fit” refers to a difference in effective diameter.

The thread cutting of the joint including the seal portion and the shoulder portion is usually performed by a computer control using an NC lathe. The above-mentioned angle can be manufactured with a practically accurate precision without special precision control by a computer-controlled NC lathe.

3. Factors Affecting the Inclination Difference θ A) The inclination difference θ set in this way is almost proportional to D / t = (outer diameter of pipe body) / (wall thickness of pipe) in the case of the inner shoulder. When D / t is large, the rigidity against bending becomes small, so that it is easy to bend and the difference in inclination is large. Therefore, it is necessary to change the magnitude of θ according to the magnitude of D / t.

B) θ is also substantially proportional to δr = (fitting amount of seal forming portion) − (fitting amount of screw forming portion). The fitting margin is a difference between the effective diameter of the pin portion and the effective diameter of the box portion, and thus causes a reduction in diameter. As described above, the “fitting of the seal forming portion” is effective for both reducing the diameter of the pin tip and bending the torque shoulder forming surface. But,
When the “fitting margin of the seal forming part” is the same as the “fitting margin of the screw forming part”, only a uniform diameter reduction occurs, and no bending occurs. The "fitting portion of the thread forming portion" near the pipe main body causes only uniform diameter reduction. The "fitting of the screw forming part"
When it is equal to, the "fitting of the seal portion" only causes its diameter reduction deformation together with the fitting of the screw portion, and is balanced. Of the “fitting of the seal forming portion”, the fitting margin (= δr) obtained by subtracting the “fitting of the screw forming portion” that does not contribute to bending causes bending deformation. Θ, which is set to be substantially equal to the bending angle of the bending toward the inner surface of the pipe, is substantially proportional to δr, which is obtained by subtracting the “fitting of the thread forming part” from the “fitting of the seal forming part”. It is effective to set the difference θ between the inclinations of the torque shoulder forming surfaces of the pin side and the box side substantially in proportion to Δr .

4. In the case of an external shoulder, as shown in FIG.
Is smaller than that of the pin-side seal forming surface 53, the box-side torque shoulder forming surface 64 is bent outward by fastening and the inclination changes. In the case of the outer shoulder, unlike the inner shoulder, the bending rigidity of the coupling is involved, so that D = coupling outer diameter and t = coupling wall thickness. The box-side tip bends and deforms because the box-side tip has a small thickness and is a free end, so that the bending rigidity at the tip of the box portion is smaller than that at the pin root. Only variation .theta.a of the inclination, or only slightly larger square than .theta.a, is set to be smaller than that of the inclination theta ₁ of the pin-side torque shoulder forming face inclination theta ₂ of the box side torque shoulder forming face. At this time, a substantially uniform contact pressure or a slightly higher contact pressure on the outer surface sides 56 and 66 and a slightly lower contact pressure on the seal forming portion sides 57 and 67 can be obtained.

As a result, in the case of the external shoulder, even if a tensile stress is applied, the external surface does not open. In addition, the above-described effect in the case of the inner shoulder is directly applied to the case of the outer shoulder.

It goes without saying that a joint having both an inner shoulder and an outer shoulder is applicable to the structure of the present invention.

In the above description, the case of the coupling system is described. However, when the present invention is applied to the integral system, one end of the pipe is provided with a male screw, a seal, and a shoulder forming surface constituting a pin member. , After the other end is overlaid, a female screw constituting a box member,
Since the seal and the shoulder forming surface may be provided, the configuration of the present invention can be applied as it is.

[0060]

Next, the effects of the present invention will be described based on embodiments.

Tables 1, 2, 3 and 4 are tables showing the inclination of the torque shoulder forming surface of the joints of the invention examples and comparative examples subjected to the tests and the types of the joints. Joints A, B, C, D, E, F, G, H, I shown in Tables 1 and 2
And J (hereinafter referred to as joint A when referring to all these joints)
) Is “D / t and δ _r are all commonly 1
7.78 and 0.4 ". The joints K and L shown in Tables 3 and 4 respectively have" D / t =
13.78, δ _r = 0.199 ”and“ D / t = 2
1.72, δ _r = 0.528 ″, the D / t and δ _r are changed to be higher and lower than those of the joint A, etc. A joint having a smaller D / t and δ _r than the joint A, etc. K is reduced substantially in proportion to the difference between θ of inclination of the torque shoulder forming face, and conversely D / t and [delta] _r is the joint a such larger joints L is set a difference in inclination θ proportionally large is there.

The joints of the invention examples shown in Tables 1 to 4 are joints of the inner shoulder, the outer shoulder, and the inner and outer shoulders shown in FIGS. 1 and 2. Comparative examples shown in Table 2 show a joint having the same inclination of the pin-side and box-side torque shoulder forming surfaces, a joint having a sealing surface or the like covered with a soft metal, and a joint having a thin lip portion provided with a smooth groove (see FIG. 5) Or, a joint (FIG. 6) in which the pin and box-side torque shoulder forming surfaces have convex and concave surfaces having different radii of curvature was investigated.

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

[Table 3]

[0066]

[Table 4]

These joints were subjected to the following tests to evaluate the performance.

B. Repetitive fastening test Lubricating grease was applied to the threaded portion and the threadless portion, and after fastening and disassembly of the joint were repeated 10 times, changes in the seal portion and the torque shoulder portion were examined.

B. Gap generation test under tensile stress After the above test, the joint was fastened, and a torque was applied in a state where an axial tensile force (245.2 ton) was applied to the pipe body so as to generate a stress equivalent to 80% of the yield strength. The presence or absence of a gap inside or outside the shoulder was investigated.

C. Corrosion test under combined load While applying the tensile stress, a mixed gas of hydrogen sulfide and carbon dioxide was sealed inside the tube including the joint.
The pressure of the mixed gas was set to 5.24 kgf / mm ^{2 at} which a stress equivalent to 80% of the yield strength was generated in the pipe body. After holding for 500 hours in this state, the joint was disassembled and the corrosion location was investigated.

Tables 5 and 6 are lists showing the test results of the above three tests (A, B and C). As shown in the table, in the comparative example, a failure occurred in any of the tests, but the joint according to the present invention showed good results in any of the tests.

[0072] Table 6 is a test result of D / t and [delta] _r joint K and joint L is varied in proportion to the difference between θ of inclination in accordance with, by substantially proportional to D / t and [delta] _r This is a result clearly showing that it is effective to change the inclination difference θ.

[0073]

[Table 5]

[0074]

[Table 6]

[0075]

The threaded joint for oil country tubular goods according to the present invention has a gap at the inner side of the torque shoulder portion for the inner shoulder or the outer side of the shoulder portion for the outer shoulder, even under a tensile load due to the weight of the connected pipe. Does not occur. For this reason, it is possible to prevent crevice corrosion caused by internal or external fluid penetrating into the joint from the gap of the torque shoulder, and since excessive plastic deformation does not occur in the torque shoulder, it can be used several tens of times. Can withstand. In the future, it will be possible to provide a highly durable joint without increasing the cost due to the increasingly severe mining conditions.

[Brief description of the drawings]

FIG. 1 is a coupling type joint having a seal portion and a torque shoulder portion, in the vicinity of an inner shoulder having a structure in which a tilt of a pin-side torque shoulder forming surface is smaller than a tilt of a box-side torque shoulder forming surface. (A) shows a seal forming surface and a torque shoulder forming surface on a pin side and a box side before fastening, and (b) shows a contact pressure distribution (calculation) generated in a seal portion and a torque shoulder portion after fastening. FIG.

FIG. 2 is a drawing showing a threaded joint for an oil country tubular good having both an inner shoulder and an outer shoulder, (a) showing a pin portion and a box portion after fastening, and (b) showing an outer shoulder shown in (a). 3 is a drawing showing a structure in which the inclination of the box-side torque shoulder forming surface is smaller than the inclination of the pin-side torque shoulder forming surface in the portion of FIG.

FIG. 3 is a drawing showing an example of a threaded joint for an oil country tubular good in the case of an inner shoulder, which is a coupling type joint having a seal portion and a torque shoulder portion, and FIG. The state where the ring is fastened is shown in FIG.
2 is a drawing showing a screw portion, a seal forming portion, and a torque shoulder forming portion of FIG.

FIG. 4 is a drawing showing a joint in which a ring-shaped packing made of a soft material is inserted between a pin-side torque shoulder forming surface and a box-side torque shoulder forming surface.

FIG. 5 is a drawing showing a joint in which the tip portion (lip portion) of the pin portion is thinned to provide high sealing performance by utilizing elastic deformation, and (a) shows the pin portion and the box before fastening. (B) shows the contact pressure distribution of the seal portion and the torque shoulder forming portion after fastening.

FIG. 6 shows a pin-side torque shoulder forming surface (convex surface).
FIG. 6 is a drawing showing a joint in which the sealing performance of the seal portion is enhanced by bulging in the tube outer radial direction generated near the tip of the pin portion due to the contact of the center of curvature of the surface (concave surface) with the box-side torque shoulder forming surface being shifted.

FIG. 7 is a view showing a state in which a pin-side torque shoulder surface is inclined by θa with respect to a box-side torque shoulder surface due to bending deformation in a diameter reducing direction generated in a pin-side seal forming portion having a large effective diameter. .

[Explanation of symbols]

θ ': Deflection angle of pin tip lip, θa: Change in inclination of pin-side torque shoulder forming surface due to bending deformation of pin-tip lip, θ ₁ : Incline of pin-side torque shoulder forming surface, θ ₂ : Box-side torque Inclination of shoulder forming surface, θ: difference between inclination of pin side and box side torque shoulder forming surface Here, in case of inner shoulder: θ = θ ₂ −θ ₁ (>
0), external shoulder: θ = θ ₁ −θ ₂ (> 0) 10: pipe body, 11: pin part, 12: male screw, 20: coupling, 21: box part, 22: female screw, 30: ring 31: smooth groove provided in the circumferential direction 32: seal forming portion at the time of fastening 33: torque shoulder forming portion at the time of fastening ・ The following symbols are limited to the case of the inner shoulder. 13: seal forming surface of pin portion, 23: seal forming surface of box portion, 14: torque shoulder forming surface of pin portion, 24: torque shoulder forming surface of box portion, 16: tube inner surface of torque shoulder forming surface of pin portion 26, an end of the box portion on the inner surface side of the torque shoulder forming surface, 17 ... an end portion of the torque shoulder forming surface of the pin portion on the seal forming side, 27 ... an end of the torque shoulder forming surface on the seal forming side Ends: • The following symbols are limited to external shoulders. 53: Seal forming surface of pin portion 63: Seal forming surface of box portion 54: Torque shoulder forming surface of pin portion 64: Torque shoulder forming surface of box portion 56: Tube outer surface of torque shoulder forming surface of pin portion 66, the end of the box on the outer surface side of the torque shoulder forming surface, 57: the end of the pin portion on the seal forming side of the torque shoulder forming surface, 67: the end of the torque shoulder forming surface on the seal forming side edge

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F16L 15/00 F16L 15/04 F16L 21/00

Claims (3)

(57) [Claims] 1. A seal forming surface (13) provided on an outer surface of a tip of a pin portion (11) having a male screw, and a seal forming surface (2) provided on an inner surface of a box (21) having a female screw.
3) to form a seal portion, and a torque shoulder forming surface (14) provided at the foremost portion of the pin;
A threaded joint for an oil country tubular good having the following features (a) and (b) , wherein an inner shoulder is formed by abutting a corresponding torque shoulder forming surface (24) provided on the box side. (A) The seal forming surfaces on the pin side and the box side are each a rotating surface, and the effective diameter of the pin side seal forming surface (13) is larger than the effective diameter of the box side seal forming surface (23). (B) The inclination (θ ₁ ) of the pin-side torque shoulder forming surface is smaller than the inclination (θ ₂ ) of the box-side torque shoulder forming surface, and the difference (θ) between the two is 0.5 ° ≦ θ ≦ 4. 0 ° is satisfied. Where θ = θ ₂ −θ ₁ 2. A seal portion formed by fitting a seal forming surface (53) provided on an outer surface at the base of a pin having a male screw and a seal forming surface (63) provided on an inner surface at a tip end of a box having a female screw. Forming an outer shoulder by abutting a torque shoulder forming surface (64) provided at the front end of the box and a corresponding torque shoulder forming surface (54) provided on the outer surface of the pin base.
A threaded joint for oil country tubular goods having the features of (a) and (c) . (A) The seal forming surfaces on the pin side and the box side are each composed of a rotating surface, and the effective diameter of the pin side seal forming surface (53) is larger than the effective diameter of the box side seal forming surface (63). (C) The inclination (θ ₁ ) of the pin-side torque shoulder forming surface is slightly larger than the inclination (θ ₂ ) of the box-side torque shoulder forming surface, and the difference (θ) between the two is 0.5 ゜ ≦ θ ≦
4.0 ° is satisfied. Where θ = θ ₁ −θ ₂ 3. The method according to claim 1, further comprising:
The threaded joint for oil country tubular goods according to claim 1 or 2 . (D) Pin side torque shoulder forming face of the slope (theta ₁₎ and Bo
Difference in the inclination (θ ₂ ) of the torque shoulder forming surface
(Θ) is approximately proportional to each of D / t and δr
If the value of D / t or δr is large,
Difference between the torque shoulder forming surface on the side and the box side
(Θ) is large, and the value of D / t or δr is small.
In this case, reduce the difference (θ) in the inclination of the torque shoulder forming surface.
Frustrate Here, D, t and δr are as follows. D = outer diameter of pipe or coupling, t = wall thickness of pipe or coupling δr = (fitting of seal forming surface in radial direction) − (screw
Fit margin in the radial direction of the forming surface)